Diantimony pentoxide sol and method for its preparation

ABSTRACT

A sol comprising diantimony pentoxide particles having a primary particle size of from 2 to 50 nm and a Sb 2 O 3 /Sb 2 O 5  weight ratio of at most 4 wt %.

[0001] The present invention relates to a method for producing adiantimony pentoxide sol having a high oxidation purity.

[0002] A diantimony pentoxide sol is one which is used as a flameretarding adjuvant for plastics, fibers, etc. as a microfiller for asurface treating agent for plastics or glass, as an inorganic ionexchanger, as a catalyst component, as a pigment component, etc.Usually, a highly concentrated sol (containing from 30 to 50 wt % ofSb₂O₅) stabilized by an organic base, is used.

[0003] Heretofore, as diantimony pentoxide sols, those obtained by thefollowing methods have been known.

[0004] Namely, a method of deionizing an alkali metal antimonate by acation exchange resin (JP-A-52-21298, U.S. Pat. No. 4,110,247,JP-B-57-11848), a method of reacting an alkali metal antimonate with aninorganic acid, followed by peptization (JP-A-60-41536, JP-A-61-227918),etc. have been known.

[0005] As a method other than the above, a method of oxidizingdiantimony trioxide with an aqueous hydrogen peroxide solution at a hightemperature has been reported (JP-B-53-20479, JP-A-52-21298,JP-A-52-123997, JP-A-52-131998).

[0006] Further, a method of adding an inorganic alkaline substance atthe time of the oxidation reaction of diantimony trioxide with anaqueous hydrogen peroxide solution, to control the particle size, hasbeen reported (JP-A-59-232921, JP-A-60-137828, JP-A-2-180717).

[0007] Further, a method for preparing a sol showing excellent stabilityat the time of preparing an organo sol, is disclosed wherein anoxidation reaction of diantimony trioxide with an aqueous hydrogenperoxide is carried out in the presence of from 0.1 to 50 wt %, as SiO₂,of an inorganic silicic compound (JP-B-7-25549).

[0008] The above-mentioned conventional methods for preparing diantimonypentoxide sols, have the following problems.

[0009] A diantimony pentoxide sol by an ion exchange method has a nearlyspherical shape and thus has a characteristics that the dispersibilityis good and the stability is also good. However, by such an ion exchangemethod, control of the particle size is difficult, and there is adrawback that a sol having a small particle size and high transparencycan hardly be obtained, or a drawback that it is difficult to preparediantimony pentoxide (Sb₂O₅) at a concentration of at least 10 wt %, andthe operation to carry out separation and regeneration of the ionexchange resin, is cumbersome.

[0010] Whereas, by the oxidation method at a high temperature, it ispossible to directly obtain a sol wherein diantimony pentoxide has ahigh concentration at a level of 30%, but it has a drawback that theviscosity tends to be high, and yet, the shape of colloidal particles isirregular shape, and the dispersibility is poor, and since the surfaceactivity is large, the compatibility with a resin emulsion tends to bepoor.

[0011] Further, as a method for improving the stability of a diantimonypentoxide sol obtained by the oxidation method, a method has beenproposed wherein an inorganic alkaline substance is added during thepreparation of the diantimony pentoxide sol to control the particlesize. However, such a reaction carried out in the presence of aninorganic alkaline substance, has a drawback that the yellow color ofthe resulting diantimony pentoxide sol tends to be intensified, andthere will be a restriction when it is to be used as a microfiller for acoating agent.

[0012] Further, a silica/antimony oxide composite sol prepared in thepresence of an inorganic silicic compound, will contain silica in itscomposition, and thus has a drawback such that the refractive index ofthe sol itself tends to decrease.

[0013] By the above-mentioned conventional oxidation method, even if thereaction is, for example, carried out in a H₂O₂/Sb₂O₃ molar ratio of 3.0i.e. in an excess amount exceeding 2.0, it is not easy to bring Sb(III)to a level of a Sb₂O₃/Sb₂O₅ weight ratio of at most 5%, and due to thisremaining Sb(III), a part of the product takes an intermediate oxidizedstate, and the yellow color tone of the resulting sol tends to beintensified (Yellow Index (YI value) tends to be high), whereby the solhas a drawback that there will be a restriction when it is to be usedfor a transparent coating material.

[0014] It is an object of the present invention to overcome theabove-mentioned problems of the conventional methods for preparing adiantimony pentoxide sol and to present a method for preparing adiantimony pentoxide sol having a high oxidation purity industrially.

[0015] In the first aspect, the present invention provides a solcomprising diantimony pentoxide particles having a primary particle sizeof from 2 to 50 nm and a Sb₂O₃/Sb₂O₅ weight ratio of at most 4 wt %.

[0016] In the second aspect, the present invention provides a method forpreparing a sol comprising diantimony pentoxide particles as defined inthe first aspect, which comprises reacting a diantimony trioxidedispersion with an aqueous hydrogen peroxide solution in the presence ofa salt of isopolyacid.

[0017] In the third aspect, the present invention provides the methodfor preparing a sol comprising diantimony pentoxide particles, accordingto the second aspect, wherein the salt of isopolyacid and the diantimonytrioxide are adjusted to be present in a ratio of MO₃/Sb₂O₃=0.15 to 10wt %, as calculated as their oxides.

[0018] In the fourth aspect, the present invention provides the methodfor preparing a sol comprising diantimony pentoxide particles, accordingto the second or third aspect, wherein the salt of isopolyacid is atungstate or a molybdate.

[0019] In the fifth aspect, the present invention provides the methodfor preparing a sol comprising diantimony pentoxide particles, accordingto any one of the second to fourth aspects, wherein hydrogen peroxideand diantimony trioxide are reacted in a H₂O₂/Sb₂O₃ molar ratio of 2.0.

[0020] Now, the present invention will be described in detail inreference to preferred embodiments.

[0021] The present invention provides a sol comprising diantimonypentoxide particles having a primary particle size of from 2 to 50 nmand a Sb₂O₃/Sb₂O₅ weight ratio of at most 4 wt %.

[0022] Here, the primary particle size is not the diameter of particlesin an agglomerated form but is a diameter of one particle asindividually separated, which can be measured by an electron microscope.

[0023] In the method for producing the above sol, the diantimonytrioxide powder as the starting material may be one having an averageparticle size of at most 100 μm, but from the viewpoint of thedispersibility and the reactivity with the aqueous hydrogen peroxidesolution, it is particularly preferably at most 10 μm, and usually, adiantimony trioxide powder having an average particle size within arange of from 1 to 5 μm is preferably employed.

[0024] The salt of isopolyacid to be used in the present invention maybe a tungstate or a molybdate.

[0025] As the tungstate, sodium tungstate (Na₂WO₄), potassium tungstate(K₂WO₄), ammonium tungstate ((NH₄)₂WO₄) or lithium tungstate (Li₂WO₄)may, for example, be mentioned and preferably employed.

[0026] As the molybdate, sodium molybdate (Na₂MoO₄), potassium molybdate(K₂MoO₄) or ammonium molybdate ((NH₄)₂MoO₄) may, for example, bementioned and preferably employed.

[0027] Further, a permanganate such as potassium permanganate (KMnO4) orsodium permanganate (NaMnO₄.3H₂O), or a bichromate such as ammoniumbichromate ((NH₄)₂Cr₂O₇), potassium bichromate (K₂Cr₂O₇) or sodiumbichromate (Na₂Cr₂O₇) will also provide similar effects. However, theyare highly hazardous as metals and colored, whereby their use islimited.

[0028] The sol comprising diantimony pentoxide particles of the presentinvention, is one obtainable by oxidizing diantimony trioxide dispersedin an aqueous medium with an aqueous hydrogen peroxide solution. Themolar ratio of the hydrogen peroxide to the diantimony trioxide ispreferably H₂O₂/Sb₂O₃ being 2.0. A molar ratio of less than 2.0 is aninadequate amount to have diantimony trioxide completely converted todiantimony pentoxide. If the molar ratio exceeds 2.0, H₂O₂ isstoichiometrically excessive, such being uneconomical and is notpreferred, since a trouble such as foaming or deterioration of the resintends to result due to the remaining excessive hydrogen peroxide, orsince in order to remove such excessive hydrogen peroxide, a treatingstep such as decomposition by a catalyst or adsorption by activatedcarbon, is required to be added.

[0029] In a case where in the present invention, diantimony trioxide andan aqueous hydrogen peroxide solution are reacted in the presence of asalt of isopolyacid, the proportion of diantimony trioxide remaining inthe formed diantimony pentoxide has been found decreased as comparedwith a case where no salt of isopolyacid is added, i.e. the remainingratio of diantimony trioxide in the formed diantimony pentoxide asrepresented by the Sb₂O₃/Sb₂O₅ weight ratio has been found decreased.Namely, in the case where no salt of isopolyacid is added, the remainingratio of diantimony trioxide in the diantimony pentoxide as representedby the Sb₂O₃/Sb₂O₅ weight ratio is 5% or higher, while in a case wherediantimony trioxide and hydrogen peroxide are reacted in the presence ofa salt of isopolyacid, the remaining ratio of diantimony trioxide asrepresented by the Sb₂O₃/Sb₂O₅ weight ratio has been found to be notmore than 4%.

[0030] This indicates that oxidation has proceeded efficiently by acatalytic activity of the salt of isopolyacid during the reaction ofdiantimony trioxide and an aqueous hydrogen peroxide solution.

[0031] With the diantimony pentoxide sol obtained by the presentinvention, the color tone improvement effect has been observed by areduction of the Yellow Index (YI value). This also indicates that theoxidation purity has been improved by the efficient oxidation. In ausual reaction of diantimony trioxide and an aqueous hydrogen peroxidesolution, even if the reaction is carried out by adjusting the molarratio of the aqueous hydrogen peroxide solution to diantimony trioxide(H₂O₂/Sb₂O₃) to be excessive as much as 3.0, it is difficult to bringthe proportion of diantimony trioxide remaining in the formed diantimonypentoxide to a level of a Sb₂O₃/Sb₂O₅ weight ratio of not more thanabout 5%.

[0032] This salt of isopolyacid is preferably added before addition ofdiantimony trioxide. To an aqueous medium having the salt of isopolyaciddispersed therein, prescribed amounts of diantimony trioxide and anaqueous hydrogen peroxide solution are added, and the reaction iscarried out with stirring. The order of addition of diantimony trioxideand the aqueous hydrogen peroxide solution is not particularly limited,but they are preferably added so that the molar ratio of hydrogenperoxide to diantimony trioxide (H₂O₂/Sb₂O₃) will readily reach a ratioof 2.0. Namely, it is preferred that after the dissolution of the saltof isopolyacid, diantimony trioxide is dispersed and finally the aqueoushydrogen peroxide solution is added.

[0033] In this reaction, addition of diantimony trioxide and the aqueoushydrogen peroxide solution is carried out by adding prescribed amountsof diantimony trioxide and the aqueous hydrogen peroxide solution. Theaddition of diantimony trioxide and the aqueous hydrogen peroxidesolution may be carried out by adopting either a method of adding all atonce or a method of carrying out the addition as divided into severaltimes. Either by the method of adding all at once or by the method ofadding dividedly in several times, the molar ratio of hydrogen peroxideto diantimony trioxide to be added every time is preferably maintainedto be H₂O₂/Sb₂O₃ being 2.0. The concentration of the aqueous hydrogenperoxide solution to be used is from 30 to 60 wt %, usually preferably35 wt %.

[0034] Further, by the addition and combined use of a compound of anelement analogous to antimony (such as phosphoric acid, ascenic acid,etc.) as a particle size-controlling material, the oxidation efficiencywill further be improved. Such an analogous element compound (such asphosphoric acid, ascenic acid or the like) may be added in an amountwithin a range of from 0 to 20 wt % based on Sb₂O₃, as calculated as anoxide represented by P₂O₅ or As₂O₅.

[0035] The amount of the salt of isopolyacid to be added during thereaction is usually from 0.15 to 10 wt %, preferably from 0.5 to 10 wt%, as calculated as its oxide MO₃ to Sb₂O₃ in a weight ratio ofMO₃/Sb₂O₃. The amount may be less than 0.15 wt %, but the effect isthereby small, and even if the amount exceeds 10 wt %, the effect ofaddition will be saturated, and such is not efficient.

[0036] The reaction temperature is usually from 30 to 100° C.,preferably from 70° C. to 100° C.

[0037] The reaction of diantimony trioxide and the aqueous hydrogenperoxide solution is an oxidation exothermic reaction. Accordingly, insome cases, it is preferred to carry out the reaction while cooling thereactor, or a reflux condenser may be installed. In the presentinvention, the reaction is carried out at a concentration of Sb₂O₃ beingfrom 1 to 20 wt %, preferably from 5 to 15 wt %. It may be less than 1wt %, but the concentration is too low, whereby the volume efficiency ofthe reactor decreases, such being uneconomical. Further, it may exceeds20 wt %, but the reaction is an oxidation exothermic reaction, wherebythe temperature control tends to be difficult, and secondaryagglomeration among particles tends to increase, whereby thedispersibility also decreases.

[0038] The diantimony pentoxide sol obtained by the present inventionhas a pH of from 2 to 4 and is stable by itself. Further, the diantimonypentoxide sol obtained by the present invention has a high oxidationpurity. Accordingly, depending upon the particularly application, inorder to control the acidity or the cation exchange ability of thesurface of the diantimony pentoxide sol, it may be treated withdiantimony trioxide or with an inorganic base such as lithium hydroxide,sodium hydroxide or potassium hydroxide to adjust the pH to a level offrom 4 to 10 to such an extent not to impair the stability of the sol.

[0039] The amount of the inorganic base to be added is such that, ascalculated as oxides, the M₂O/Sb₂O₅ molar ratio is from 0 to 0.8. If themolar ratio exceeds 0.8, the inorganic base tends to be excessive, andthe stability of the sol tends to deteriorate. The amount of diantimonytrioxide to be added may depend also on the particle size, but theSb₂O₃/Sb₂O₅ molar ratio is from 0 to 0.4, and if the molar ratio exceeds0.4, the controlling effect will be saturated.

[0040] As a result of the measurement of X-ray diffraction, one havingthe sol surface treated with diantimony trioxide was confirmed to have astructure of hydrated diantimony pentoxide (Sb₂O₅.nH₂O) and to be not anintermediate oxide such as Sb₆O₁₃.

[0041] Further, it is possible to improve the dispersion stability byadding an organic base or a carboxylic acid. The organic base to be usedin the present invention, may, for example, be an alkanolamine such astriethanolamine or monoethanolamine, an alkylamine such as n-propylamineor diisopropylamine, quaternary ammonium hydroxide or guanidinehydroxide. Among them, particularly preferred is an alkylamine. Theamount of the organic base to be added, is usually from 1 to 30 wt %,preferably from 2 to 20 wt %, based on Sb₂O₅. It may be added in anamount exceeding 30 wt %, but there will be no further improvement inthe dispersing effect.

[0042] The carboxylic acid to be used in the present invention, may, forexample, be a monocarboxylic acid such as formic acid or acetic acid, adicarboxylic acid such as oxalic acid, malonic acid, succinic acid,glutaric acid, adipic acid or maleic acid, or an oxycarboxylic acid suchas lactic acid, tartaric acid, citric acid, glycolic acid, malic acid,gluconic acid or mandelic acid. Among them, particularly preferred is anoxycarboxylic acid. The amount of the carboxylic acid to be added, isusually from 0 to 30 wt %, preferably from 0.5 to 10 wt %, based onSb₂O₅.

[0043] Further, in a case where it is desired to increase theconcentration of the obtained sol, such concentration can be done by ausual method such as an evaporation method or an ultrafiltration method.Further, in order to increase the stability of the sol, it is preferredthat the pH is adjusted to from 5 to 8 by means of the above-mentionedorganic base or carboxylic acid, followed by concentration.

[0044] In the above modified diantimony pentoxide sol, the dispersingmedium may be changed from water to a hydrophilic organic solvent. Sucha hydrophilic organic solvent may, for example, be a lower alcohol suchas methanol, ethanol or isopropanol, a linear amide such asdimethylformamide or N,N-dimethylamide, a cyclic amide such asN-methyl-2-pyrrolidone, a glycol ether such as methylcellosolve,ethylcellosolve, butylcellosolve or carbitol, or a polyhydric alcoholsuch as ethylene glycol or glycerol.

[0045] The above-mentioned change from water to the hydrophilic organicsolvent may be carried out by a usual method, such as a reduced pressureor normal pressure distillation substitution method or a substitutionmethod by means of an ultrafilter.

[0046] Now, the present invention will be described in further detailwith reference to Examples and Comparative Examples. However, it shouldbe understood that the present invention is by no means restricted tosuch specific Examples.

EXAMPLE 1

[0047] In a 2 L reaction flask equipped with a stirrer, in 1,693.1 g ofpure water, 10.42 g (containing 7.20 g as calculated as WO₃) of sodiumtungstate dihydrate (Na₂WO₄.2H₂O, manufactured by Kisan KinzokuChemicals Co., Ltd., containing 69.1 wt % as calculated as WO₃) wasdissolved, then 130.4 g of diantimony trioxide (Sb₂O₃ content: 99.5 wt%, manufactured by Guangdong Mikuni Antimony Industries, Co., Ltd.) wasdispersed, and then 86.6 g of a 35 wt % hydrogen peroxide aqueoussolution was added, whereupon the mixture was heated and reacted. TheH₂O₂/Sb₂O₃ molar ratio was 2.0, and the proportion of WO₃/Sb₂O₃ was 5.5wt %.

[0048] The liquid temperature during the reaction was from 85 to 90° C.After completion of the reaction, stirring was maintained at 90° C. forone hour to obtain 1,906 g of a yellowish white sol. The obtained solhad a primary particle size of from 15 to 25 nm, a pH of 2.50, anelectroconductivity of 575 μs/cm, a Sb₂O₅ content of 7.28 wt %, a Sb₂O₃content of 0.20 wt % and a remaining ratio (Sb₂O₃/Sb₂O₅) of 2.7 wt %.

EXAMPLE 2

[0049] In a 2 L reaction flask equipped with a stirrer, in 1,688 g ofpure water, 10.42 g (containing 7.20 g as calculated as WO₃) of sodiumtungstate dihydrate (Na₂WO₄.2H₂O, manufactured by Kisan KinzokuChemicals Co., Ltd., containing 69.1 wt % as calculated as WO₃) wasdissolved, then 130.4 g of diantimony trioxide (Sb₂O₃ content: 99.5 wt%, manufactured by Guangdong Mikuni Antimony Industries, Co., Ltd.) wasdispersed, and then 5.14 g of a 85 wt % phosphoric acid aqueous solutionand 86.6 g of a 35 wt % hydrogen peroxide aqueous solution were added,whereupon the mixture was heated and reacted. The H₂O₂/Sb₂O₃ molar ratiowas 2,0, and the proportion of WO₃/Sb₂O₃ was 5.5 wt %, and theP₂O₅/Sb₂O₃ weight ratio was 2.4 wt %.

[0050] The liquid temperature during the reaction was from 85 to 90° C.After completion of the reaction, stirring was maintained at 90° C. forone hour to obtain 1,903 g of a slightly yellow sol. The obtained solhad a primary particle size of from 8 to 15 nm, a pH of 2.22, anelectroconductivity of 2,910 μs/cm, a Sb₂O₅ content of 7.46 wt %, aSb₂O₃ content of 0.04 wt %, and a remaining ratio (Sb₂O₃/Sb₂O₅) of 0.5wt %. To 1,509.4 g of this sol, 22.4 g of a 25% NaOH aqueous solution,6.6 g of diisopropylamine and 0.94 g of tartaric acid were added,adjusted and concentrated by a rotary evaporator to obtain 333.2 g of amodified diantimony pentoxide aqueous sol. The obtained sol had aspecific gravity of 1.484, a pH of 4.66, a total Sb₂O₅ content of 34.0wt % and a Yellow Index (YI value) of 59.8 as measured by a colordifference meter (transmitted light).

EXAMPLE 3

[0051] In a 1 L reaction flask equipped with a stirrer, in 788.1 g ofpure water, 1.94 g (containing 1.34 g as calculated as WO₃) of sodiumtungstate dihydrate (Na₂WO₄.2H₂O, manufactured by Kisan KinzokuChemicals Co., Ltd., containing 69.1 wt % as calculated as WO₃) wasdissolved, then 60.68 g of diantimony trioxide (Sb₂O₃ content: 99.5 wt%, manufactured by Guangdong Mikuni Antimony Industries, Co., Ltd.) wasdispersed, and then 2.39 g of a 85% phosphoric acid aqueous solution and40.27 g of a 35 wt % hydrogen peroxide aqueous solution were added,whereupon the mixture was heated and reacted. The H₂O₂/Sb₂O₃ molar ratiowas 2,0, the proportion of WO₃/Sb₂O₃ was 2.2 wt %, and the P₂O₅/Sb₂O₃weight ratio was 2.4 wt %.

[0052] The liquid temperature during the reaction was from 80 to 95° C.After completion of the reaction, stirring was maintained at 90° C. forone hour to obtain 886.5 g of a slightly yellow sol. The obtained solhad a primary particle size of from 8 to 15 nm, a pH of 2.2, anelectroconductivity of 2,230 μs/cm, a WO₃ content of 0.15 wt %, a Sb₂O₅content of 7.27 wt %, a Sb₂O₃ content of 0.21 wt % and a remaining ratio(Sb₂O₃/Sb₂O₅) of 2.9 wt %.

EXAMPLE 4

[0053] In a 10 L reaction flask equipped with a stirrer, in 8,478 g ofpure water, 10.42 g (containing 7.20 g as calculated as WO₃) of sodiumtungstate dihydrate (Na₂WO₄.2H₂O, manufactured by Kisan KinzokuChemicals Co., Ltd., containing 69.1 wt % as calculated as WO₃) wasdissolved, then 652.0 g of diantimony trioxide (Sb₂O₃ content: 99.5 wt%, manufactured by Guangdong Mikuni Antimony Industries, Co., Ltd.) wasdispersed, and then 25.72 g of a 85% phosphoric acid aqueous solutionand 432.7 g of a 35 wt % hydrogen peroxide aqueous solution were added,whereupon the mixture was heated and reacted. The H₂O₂/Sb₂O₃ molar ratiowas 2,0, the proportion of WO₃/Sb₂O₃ was 1.1 wt %, and the P₂O₅/Sb₂O₃weight ratio was 2.4 wt %.

[0054] The liquid temperature during the reaction was from 80 to 95° C.After completion of the reaction, stirring was maintained at 90° C. forone hour to obtain 9,596 g of a slightly yellow sol. The obtained solhad a primary particle size of from 8 to 15 nm, a pH of 2.1, anelectroconductivity of 2,130 μs/cm, a WO₃ content of 0.075 wt %, a Sb₂O₅content of 7.21 wt %, a Sb₂O₃ content of 0.26 wt % and a remaining ratio(Sb₂O₃/Sb₂O₅) of 3.6 wt %.

EXAMPLE 5

[0055] In a 3 L reaction flask equipped with a stirrer, in 2,117.9 g ofpure water, 1.54 g (containing 0.90 g as calculated as MoO₃) of sodiummolybdate (Na₂MoO₄.2H₂O, manufactured by Junsei Chemical Co., Ltd.,containing 58.6 wt % as calculated as MoO₃) was dissolved, then 163.0 gof diantimony trioxide (Sb₂O₃ content: 99.5 wt %, manufactured byGuangdong Mikuni Antimony Industries, Co., Ltd.) was dispersed, and then6.43 g of a 85% phosphoric acid aqueous solution and 108.2 g of a 35 wt% hydrogen peroxide aqueous solution were added, whereupon the mixturewas heated and reacted. The H₂O₂/Sb₂O₃ molar ratio was 2,0, theproportion of MoO₃/Sb₂O₃ was 0.55 wt %, and the P₂O₅/Sb₂O₃ weight ratiowas 2.4 wt %.

[0056] The liquid temperature during the reaction was from 80 to 95° C.After completion of the reaction, stirring was maintained at 90° C. forone hour to obtain 2,396.0 g of a slightly green sol. The obtained solhad a primary particle size of from 10 to 15 nm, a pH of 2.2, anelectroconductivity of 1,530 μs/cm, a MoO₃ content of 0.15 wt %, a Sb₂O₅content of 7.26 wt %, a Sb₂O₃ content of 0.22 wt % and a remaining ratio(Sb₂O₃/Sb₂O₅) of 3.0 wt %.

EXAMPLE 6

[0057] Into a 3 L reaction flask equipped with a stirrer, 2,399 g of thesol obtained in Example 4 was charged, and 35.6 g of a 25% NaOH aqueoussolution, 14.4 g of diisopropylamine and 2.70 g of tartaric acid wereadded with stirring, whereupon concentration was carried out by means ofan ultrafilter, to obtain 524.7 g of a modified diantimony pentoxideaqueous sol. The obtained sol had a specific gravity of 1.454, a pH of4.83, a total Sb₂O₅ content of 34.3 wt % and a yellow Index (YI value)of 60.2 as measured by a color difference meter (transmitted light).Further, 359.6 g of this sol was put into a 1 L reaction flask equippedwith a stirrer, and water was distilled off while gradually adding 3 Lof methanol under atmospheric pressure, to obtain 365 g of a modifieddiantimony pentoxide methanol sol having water of the aqueous solsubstituted by methanol. This sol had a primary particle size of from 8to 15 nm, a specific gravity of 1.146, a viscosity of 1.8 mPa·s, a pH of8.3, a total Sb₂O₅ content of 32.1 wt %, a water content of 2.5% and atransmittance of 52%.

EXAMPLE 7

[0058] Into a 10 L reaction flask equipped with a stirrer, 7,197 g ofthe sol obtained in Example 4 was charged, and heated to a liquidtemperature of from 90 to 95° C., whereupon 97.8 g of diantimonytrioxide was added in a (Sb₂O₃ (modified content))/(Sb₂O₅ (sol content))molar ratio of 0.2, followed by further aging at 90° C. for one hour formodification. The obtained sol had a pH of 2.18, an electroconductivityof 1,850 μs/cm, a total Sb₂O₅ content of 8.9 wt %, and a particle sizeof from 7 to 12 nm as observed by an electron microscope. To this sol,99.5 g of a 25% NaOH aqueous solution, 45.4 g of diisopropylamine and5.3 g of tartaric acid were added, adjusted and concentrated by anultrafilter to obtain 1,631.1 g of a modified diantimony pentoxideaqueous sol. The obtained sol had a primary particle size of from 10 to15 nm, a specific gravity of 1.526, a pH of 6.02, and a total Sb₂O₅content of 38.0 wt %. Further, this sol was transferred to a 3 Lreaction flask equipped with a stirrer, and water was distilled offwhile gradually adding 13 L of methanol, to obtain 2,000 g of a modifieddiantimony pentoxide methanol sol having water of the aqueous solsubstituted by methanol. This sol had a specific gravity of 1.134, aviscosity of 1.3 mPa·s, a pH of 6.4, a total Sb₂O₅ content of 30.8 wt %,a water content of 2.9% and a transmittance of 74%.

COMPARATIVE EXAMPLE 1

[0059] In a 1 L reaction flask equipped with a stirrer, in 792.9 g ofpure water, 60.33 g of diantimony trioxide (Sb₂O₃ content: 99.5 wt %,manufactured by Guangdong Mikuni Antimony Industries, Co., Ltd.) wasdispersed, and then 40.07 g of a 35 wt % hydrogen peroxide aqueoussolution was added, whereupon the mixture was heated and reacted. TheH₂O₂/Sb₂O₃ molar ratio was 2.0.

[0060] The liquid temperature during the reaction was from 85 to 95° C.After completion of the reaction, stirring was maintained at 90° C. forone hour to obtain 885.0 g of a yellowish white sol. The obtained solhad a primary particle size of from 15 to 25 nm, a pH of 2.1, anelectroconductivity of 430 μs/cm, a Sb₂O₅ content of 6.83 wt %, a Sb₂O₃content of 0.60 wt %, and a remaining ratio (Sb₂O₃/Sb₂O₅) of 8.8 wt %.To 800 g of this sol, 11.9 g of a 25% NaOH aqueous solution, 4.2 g ofdiisopropylamine and 0.61 g of tartaric acid were added, adjusted andconcentrated by a rotary evaporator to obtain 185.1 g of a modifieddiantimony pentoxide aqueous sol. The obtained sol had a specificgravity of 1.416, a pH of 4.22, a total Sb₂O₅ content of 32.4 wt % and aYellow Index (YI value) of 145.2 as measured by a color difference meter(transmitted light).

COMPARATIVE EXAMPLE 2

[0061] In a 1 L reaction flask equipped with a stirrer, in 785.8 g ofpure water, 60.33 g of diantimony trioxide (Sb₂O₃ content: 99.5 wt %,manufactured by Guangdong Mikuni Antimony Industries, Co., Ltd.) wasdispersed, and then 2.49 g of a 85% phosphoric acid aqueous solution and40.07 g of a 35 wt % hydrogen peroxide aqueous solution were added,whereupon the mixture was heated and reacted. The H₂O₂/Sb₂O₃ molar ratiowas 2,0, and the P₂O₅/Sb₂O₃ weight ratio was 2.4 wt %.

[0062] The liquid temperature during the reaction was from 80 to 95° C.After completion of the reaction, stirring was maintained at 90° C. forone hour to obtain 887.5 g of a yellow sol. The obtained sol had aprimary particle size of from 10 to 15 nm, a pH of 2.1, anelectroconductivity of 1,830 μs/cm, a Sb₂O₅ content of 7.08 wt %, aSb₂O₃ content of 0.38 wt %, and a remaining ratio (Sb₂O₃/Sb₂O₅) of 5.4wt %.

[0063] The diantimony pentoxide sol of the present invention is usefulas a flame retardant adjuvant for plastics, fibers, etc., or forinorganic ion exchangers, etc. Further, one having a primary particlesize of the sol being from 5 to 30 nm, is excellent in transparency anddispersibility and thus, is useful as a microfiller for a coating agentwhich is useful for shielding ultraviolet rays or for adjusting therefractive index by coating it on the surface of a transparent substratesuch as plastics or glass.

[0064] The entire disclosure of Japanese Patent Application No.2003-086901 filed on Mar. 27, 2003 including specification, claims andsummary is incorporated herein by reference in its entirety.

What is claimed is:
 1. A sol comprising diantimony pentoxide particles having a primary particle size of from 2 to 50 nm and a Sb₂O₃/Sb₂O₅ weight ratio of at most 4 wt %.
 2. A method for preparing a sol comprising diantimony pentoxide particles as defined in claim 1, which comprises reacting a diantimony trioxide dispersion with an aqueous hydrogen peroxide solution in the presence of a salt of isopolyacid.
 3. The method for preparing a sol comprising diantimony pentoxide particles, according to claim 2, wherein the salt of isopolyacid and the diantimony trioxide are adjusted to be present in a ratio of MO₃/Sb₂O₃=0.15 to 10 wt %, as calculated as their oxides.
 4. The method for preparing a sol comprising diantimony pentoxide particles, according to claim 2, wherein the salt of isopolyacid is a tungstate or a molybdate.
 5. The method for preparing a sol comprising diantimony pentoxide particles, according to claim 2, wherein hydrogen peroxide and diantimony trioxide are reacted in a H₂O₂/Sb₂O₃ molar ratio of 2.0. 